Canine hypoadrenocorticism is a rare syndrome in dogs characterized by a deficiency of adrenal cortex hormones, usually both glucocorticoids and mineralocorticoids (Addison’s disease). Most affected dogs have primary hypoadrenocorticism, most commonly due to immune-mediated destruction of the adrenal cortex. Diagnostic tests used to confirm the diagnosis of hypoadrenocorticism, such as the ACTH response test, are discussed along with the different treatment options, including glucocorticoid and mineralocorticoid replacement therapy. Guidance is provided on managing acute and chronic cases. The prognosis for dogs with hypoadrenocorticism is usually good with proper management and lifelong treatment.